The present invention relates generally to a system for unloading granular materials from a ship, and more particularly pertains to a system for unloading grandular materials from an oil tanker which has been put into service carrying granular materials.
Present political and economic situations around the world have resulted in a surplusage of oil tankers. Concurrently there has been a rising demand for shipment of wheat to various areas of the world. In view of the surplusage of oil tankers and the demand for shipment of wheat, it would be desirable to be able to transport wheat in vessels designed for the carriage of oil. Oil tankers may be readily loaded with a wheat cargo, but there is a problem with unloading the wheat. A vessel designed for the carriage of granular materials such as wheat typically has large hatches through which conveyor equipment may gain access to the wheat cargo. This enables a rapid and efficient unloading of the cargo. Unfortunately, oil tankers do not have sufficiently wide hatches to allow such conveyor equipment access to the holds.
One method used in the prior art to unload wheat from an oil tanker has utilized VACUVATOR equipment, which is in the nature of a giant vacuum cleaner. This equipment is introduced into the oil tanker holds through existing hatches, and the wheat is vacuumed out of the hold during offloading. A problem with this approach is that it is too time consuming, and with this approach three to four weeks may be required to unload a large oil tanker.
Present oil tankers are built with some unique structure, some of which is taken advantage of by the present invention. Many oil tankers are designed to be pressurized, and as a safety factor, the top of each hold is designed to support eight feet of water in the event of waves breaking across the ship. Many oil tankers also include large blowers which are connected to each hold by pipes, and are utilized during several types of operations on an oil tanker. After the holds are filled with oil, the blowers are utilized to fill the remaining spaces in the holds with boiler flue gas, an inert gas, to minimize the possibility of combustion in the holds. After unloading, the blowers are also utilized to flush residual gases out of the holds.